Japanese Laid-Open Patent Publication No. 2007-296817 (Document 1) discloses a method of applying a voltage to a pressure generator constructed by layering a piezoelectric element that uses PZT (lead zirconate titanate) or the like, a metal plate and ceramics to generate pressure and thereby cause a liquid to be discharged. In addition, Document 1 discloses a method that uses the above method, has a slender cylindrical piezoelectric body with a diameter of around 0.1 to 1 mm provided midway from a tank to a discharge outlet, and causes droplets to be expelled by having such part function as a pressurizing pump. This is called a Gould-type ink jet head and has electrodes formed on an inner surface and an outer surface of the cylindrical piezoelectric body with lead wires that apply the driving voltage being connected. The inner surface electrode of the cylindrical piezoelectric body is attached to a hollow pipe that passes through such cylindrical piezoelectric element by adhesive. To avoid an electrical connection with the cylindrical piezoelectric body, the hollow pipe is constructed of an insulating material such as glass, an ink tube for supplying ink from an ink tank or the like is connected to one end of the hollow pipe, and a discharge outlet for discharging ink droplets is formed at the other end.
Research is being carried out into discharging ink and other substances onto printing paper and alternative materials and mediums using ink jet technologies developed as printer apparatuses. With a method that uses an actuator such as a piezo element, since discharging is possible without heating the liquid, a wide range of applications is anticipated. The substance to be discharged is not limited to liquid and research is being conducted into a wide variety of substances including a mixture of liquid and particles (a liquid substance) that may include an aqueous solution, a solvent, a reagent, a living (living body) material such as cells or genes, and the like. Accordingly, there is demand for a discharge head that is compatible with liquids from a low viscosity to a high viscosity, a discharge head that is compatible with high surface tension and capable of discharging even pure water, and a discharge head that is resistant to acids and solvents.
Tubular members that include glass tubes, resin tubes, ceramic tubes, and metal tubes, and in particular glass tubes are commonly used as pipettes and the other instruments in experiments and the other jobs that use reagents and are suited to handling a wide variety of solutions. Accordingly, a Gould-type ink jet head in which a glass tube and a cylindrical piezoelectric body are combined is one example of a head that can satisfy the above demands. A method of forming a piezoelectric layer directly on a glass tube by sputtering, screen printing, gas deposition, or the like to form a cylindrical piezoelectric element along the glass tube, a method where a piezoelectric ceramic is sintered and the center thereof is removed by cutting, and a method of sintering in a cylindrical shape are applicable. However, regardless of which method is used, it is not very easy or economical to efficiently apply pressure to a glass tube using a Gould-type ink jet head. In particular, since it is necessary to make the inner diameter of the piezoelectric element only slightly larger than the diameter of the tube, it is necessary to match the inner diameter of the piezoelectric element in a range of several μm to several hundred μm to fluctuations in the outer diameter of the tube, which has caused an increase in cost and a drop in yield.